The present invention relates generally to endless or cyclical conveyors and more particularly to those equipped with self-supporting, load-transporting platforms.
Vertical conveyors and other endless conveyors which move goods in a multi-directional pattern are typically equipped with several relatively spaced apart, load-transporting platforms and with sets of endless drive chains and sprockets which define the cyclical drive chain pattern that the platforms follow. The platform is somewhat like a suspension bridge because it is supported at its opposite ends, but not in the middle, and must not sag appreciably when it is carrying a load. In some ways, the subject platform is more complex than a suspension bridge because the platform carries the load up and/or down and must be able to bend when it follows the chain drives around the sprockets back to a starting position.
In order to be both rigid when carrying a load and flexible when returning to the start, the conventional platform is made up of a series of parallel, laterally extending, interconnected segments. Each segment consists of a long shaft or tube, a pair of stop blocks and a pair of link members. Each of the opposing outer ends of the long shaft is sandwiched between one of the stop blocks and one of the link members. Adjacent segments are pivotally connected together by their link members, and the link members define the turning points which enable the platform to bend as it follows the drive chains around the sprockets. The stop blocks are sized, shaped and positioned so that they engage one another when the platform is in a flat, load-receiving configuration. The stop blocks are substantially incompressible, so, when they come together, they act collectively like a unitary, rigid beam on each side of the platform to stop the platform from sagging under the weight of a load.
The stop blocks separate from one another when the unloaded platform follows the curves defined by the drive chain sprockets. This separation is somewhat like the movement of the outer plates on a metal watchband when the band is being flexed. However, the separation is only momentary, because the platform is moving relatively rapidly through the curve and back into a flat or planar configuration. The angular gap between adjacent segments of the platform closes rapidly, whereupon the incompressible blocks on the adjacent segments strike one another. The rapid re-engagement of the stop blocks creates noise and wear. Since there are many stop blocks on each side of the platform, several curves through which the platform passes on each cycle and several platforms on the vertical conveyor, the noise and wear caused by any two of the stop blocks striking each other are multiplied many times while the conveyor is running.
In the past, the problems of stop block noise and wear were addressed in several ways. One approach was to limit the speed of the conveyor. In this manner, the velocity at which adjacent stop blocks struck one another was low enough to limit noise and wear to acceptable levels. However, this approach was inherently unsatisfactory because the demand for faster vertical conveyors was not being met, even though the conveyor was otherwise capable of operating at higher speeds. Another effort to solve the problem required the alternation of steel and nylotron stop blocks, based upon the expectation that the nylotron would have noise dampening and wear reducing effects. The interposition of nylotron blocks between the steel stop blocks worked well enough when first installed, but the steel blocks wore down the nylotron too quickly. Yet another proposed solution was to inject urethane foam into the hollow transverse tubes of the platform, on the theory that the sound waves generated by the stop blocks clapping together were resonating in the hollow tubes. However, this experiment did not reduce wear, nor did it significantly reduce the noise level.
Thus, the present inventor(s) was/were confronted with the problems of reducing the noise and wear caused by the stop block collisions without limiting the speed, safety and reliability of the conveyor or driving the production and assembly costs excessively high.